A time slip is a plot device in fantasy and science fiction in which a person, or group of people, seem to travel through time by unknown means. The idea of a time slip was used in 19th century fantasy, an early example being Washington Irving's 1819 Rip Van Winkle, where the mechanism of time travel is an extraordinarily long sleep. Time-slip stories were popularized at the end of the century by Mark Twain's 1889 historical novel A Connecticut Yankee in King Arthur's Court, which had considerable influence on later writers. The plot device is also popular in children's literature.